But the BUSS has not been designed to exit a fully developed stall. BUSS is not the solution either to unreliable speed indication above 25000 feet.
As you said the BUSS is activated by switching off all 3 AirData sources, this action will also force the flight control Alternate Law.
Its advised to not use it above FL250 because theres the assumption there is sufficient altitude to recover an UAS.
From the FCTM:
‐ At high altitude, typically above FL 250, the cases of unreliable speed situation are mostly a
temporary phenomenon: They are usually due to contamination of the pitots, by water or ice,
in particular meteorological conditions. In-service experience shows that such a contamination
typically disappears after few minutes, allowing to recover normal speed indications.
Would the AF447 crew have attempted to select all ADRs OFF passing FL250 in order to activate the BUSS ... ?
It comes with an ECAM drill...then the question is:
Would the AF447 crew had followed the drill passing FL250?
What would have been the BUSS indication ?
The yellow AOA indicator line [Current AOA] would have been at the bottom of the SLOW side of the scale.
Is it designed for 45 deg of AoA ?
It is based on Inertial data instead of AirData and always available as long IRs not failed, since the AOA is now also available when AirData is not (e.g. CAS <60Kts)
the stall warning would not have silenced.
I have some doubt about the BUSS ... but I have never experienced it in the simulator.
A more simple AoA indicator could be a better option maybe ...
Maybe, but the AOA limit (in Alternate and Direct Law) is a function of MACH, Speedbrake and Flap/Slat settings.
Then a crew needs to know its limits for MACH/CONFIG or the bug needs to be automated and that will make it more than just a simple indicator.
BTW The BUSS is not adopted for use of Speedbrake